1. Field of the Invention
The present invention relates to a sheet feeding apparatus and an image forming apparatus, and more particularly, to a sheet feeding apparatus including a detachably-mounted feed roller for feeding a sheet.
2. Description of the Related Art
Conventionally, in an image forming apparatus such as a printer, a copying machine, or a facsimile machine, there is provided a sheet feeding apparatus for separating and feeding sheets one by one from a sheet stacking unit in which multiple sheets are stacked. In the sheet feeding apparatus, there is provided a feed roller for feeding the uppermost sheet among the stacked sheets. However, there is a possibility that an outer peripheral surface of the feed roller may deteriorate after being used for a long time due to abrasion or the like, causing a decrease in feeding performance. For this reason, the feed roller is made to be detachable from the sheet feeding apparatus so as to be periodically replaced with ease.
In order to facilitate replacement work of the feed roller by a user or a service person, there is conventionally known a sheet feeding apparatus having a structure in which the feed roller is made into a unit, and one shaft and a main body of the feed roller can make a slide movement relative to each other. With the above-mentioned structure, the main body of the feed roller is caused to relatively slide with respect to the one shaft, and engagement with the shaft of the apparatus main body is released, whereby the feed roller can be detached. The above-mentioned structure is described in Japanese Patent Application Laid-Open No. 2004-256287.
However, the structure in which the feed roller is replaced in a slide system has the following problems.
(1) When a jam is caused in a state where a sheet is nipped between the feed roller and a sheet separating unit (separating pad or separating roller), a problem arises in a case of the jam recovery. In this case, bending or slacking of the jammed sheet is caught at an end of the feed roller, and thus the feed roller is caused to slide unnecessarily.
(2) When a mounting direction of a sheet feeding cassette is the same as a slide direction of the feed roller, a problem arises in the case where a jam is caused in a state where the sheet is nipped between the feed roller and the sheet separating unit. In this case, the jammed sheet causes the feed roller to slide if the sheet feeding cassette is drawn out.
(3) When an unexpected large force is exerted when being transported, the feed roller is detached.
In the case where the feed roller is reluctantly detached under the above-mentioned circumstances for the above-mentioned reasons, the sheet cannot be fed out, and thus the sheet feeding apparatus is judged that a failure has occurred.
In order to prevent the feed roller from being detached reluctantly, it is conceivable to provide a lock member for restricting slide movement of the feed roller. When the lock member is provided, in replacing the feed roller, the user manually switches the lock member from a lock position to a lock release position, and then replaces the feed roller. After the feed roller is replaced, the lock member is manually switched from the lock release position to the lock position.
When the lock member is provided, however, there may be a case where the user forgets to switch the lock member from the lock release position to the lock position after replacing the feed roller. In this case, feed roller is, for example, deviated or detached during feeding the sheet by the feed roller, leading to a feeding malfunction.
In order to solve the above-mentioned problems, there is known a sheet feeding apparatus in which a pivotal lock lever is provided as a lock member in a vicinity of the feed roller. In this case, even when the user forgets to switch the lock member to the lock position, the lock lever is pivoted as a result of mounting of the sheet feed cassette and is switched to the lock position automatically. This technology is described in Japanese Patent Application Laid-Open No. 2007-176621.
There is known a conventional sheet feeding apparatus in which the feed roller is replaced from the use of other opening or closing door without detaching the sheet feeding cassette. In this sheet feeding apparatus, the feed roller is replaced while the sheet feeding cassette is not attached or detached. Therefore, the lock member is not reset to the lock state by the sheet feeding cassette in the case where the user forgets to return the lock lever.
The above-mentioned structure is not provided with a countermeasure which is taken when the user forgets to set the lock lever to the lock position after the feed roller is replaced.